Discharge tube



March 5., 1'935.

G. lSGHLJBERT DISCHARGE TUBE Filed Dec. e, 19:52

3 Sheets-Sheet l aba-4215062125@ m4 I /n ventop:

' www@ G. SCHUBERT DISCHARGE TUBE March @35 Filed Deo. 6, 1952 3Sheets-Sheet 2 19o 120 isa 1'40 150 16a March 5` l935- G. SCHUBERT.DISCHARGE TUBE Filed Dec. 6, 1952 5 Sheets-Sheet 3 Gene/'afar' PatentedMar.j5, 1935 UNITED STATES DISCHARGE TUBE v Georg Schubert, Berlin,

Germany, assignor to firm Fernseh Aktien-Gesellschaft, Zehlendorf,

, near Berlin, Germany Application December 6,

i932, serial Nn. 645,980

In Germany December 1 2,A 1931 6 Claims. (Cl. 176-124) 'I'he inventionrelates to a method. of controlling discharge tubes of the positivecolumn type for television purposes. f

'Ihe mai object of the invention is to control -5 v discharge tu esfilled with sodium 4vapor and having a positive luminous column byadjusting the operating temperature of the tube in such manner that thelight density ofthe luminous column is substantially a linear functionof the grid volt- L age of the lthermionic valve which controls thedischarge tube and normallyforms the output Valve of the receiveramplifier.

In ordento receive'an undis'torted reproduction of televisiontransmission it is essential, that not ,5 only all parts of thetransmission system operate? faultlessly, but also that the intensity ofthe controlled source of light at the receiver v ariesV in proportion tothe iiuctuations of the grid potential of the output tube of thereceiver amplifier.

Assuminthat the controlled source of light is arranged inthe anodecircuit of this output tube, which is the most simplied arrangement,

then the above condition is fulfilled provided a linear function exis onone hand between theY ,5 grid potential and the anode current, and onthe other hand between e anode current and the intensity of light. Forthe purpose of obtaining,- proportionality between the fluctuations 'ofthe grid potential and the fluctuations of the anode 0 current it isnecessary that the working characteristic be a straight line, whichinturn'occurs only whenwhile operating inthe straight region of thestatic characteristic of the tube-the A'. C.

Q resistance of the anode circuit (in this case substantially thecontrolled source of light) is constant.

While it was not difllcult to yfulfill these conditions when employingthe well known sources of light such as glow lamps and kino lamps, itwas 0 at first extremely dicult to operate discharge tubes of thepositive-column type, for example the new Na-surface lamps, which onlyvery rei cently have been employed for television purposes. It is now anyimportant object of the present 3 invention .to overcome-thesedifficulties'encountered in the control of discharge tubes filled withysodium vapor. Experiments have shown that the A. C. resistance ofthese'sodium lled lamps is not constant, and furthermore that there 1sno l linear function between their intensity 'of light and the strengthof their operating current. According to the invention, however, thesediilculties mayf be largely overcome by Aoperating the lamp at apredetermined and properly adjusted i operating temperature. In. thefollowing the inventi/on is described by way of example based onexperiments made with Na-surface lamp. The same considerations, however;apply also to other discharge tubes having a positive column and aheated cathode. i

As well known, tsea-surface lamp is operated with an additional exteriorheating-means. Other discharge tubes,N however, need only be providedwith some heat protecting means to prevent ex-` cessive loss of heat andto nablethe tube' to 10 create its own operating temperature, In -theselast vmentioned tubes the adjustment of therequired operatingtenfperature according to the inventionmayfbe obtained by suitablyselecting an `average operating current. n ,'15

In the drawings: l

Fig. 1 shows thestatic resistance characteris-` tic of anA Na-surfacelamp at three different op- .eratingx temperatures. It willfbe notedthat all three characteristics are descending, only the one taken at180* C., is approximately linear, so vthat in this case the A. C.resistance is practically constant within a certain range of current. v

Fig. 2 lshows the relationshiplbetween the intensity of light and thecurrent intensity at the three operating temperatures recorded in Fig. 1and it can be seen that only .when in this particular lamp the operatingtemperature is 180 C., the light intensity is a linear function of thecurrent intensity, Whereas the same deviates very l3() appreciably ,fromthe desiredproportionality at temperatures which are only above or belowthis value.

Fig. 3 shows the relationship between the light f intensity. and theoperating temperature at three different currents. It can be seen thatat an operating temperature of 180 C. (which has been 'foundto be mostfavorable) the maximum current amplitudes vof approximately- 1D0-'140milliampere (at an average supply current of approxi- 40 mately 450-'70milli-ampere) ,'v produce approximately the maximum intensity' of lightwhich the lamp maycreate at its best. According to the invention, thedischarge tubes are maintained during their operation at .atemperature-at' which 45 (1) 'the light' intensity varies in proportionto the current intensity, (2) the A. C. resistance is approximatelyconstant, and y(3) approximately the maximum light intensity isobtained. Obviously, the condition that the A. C. resistance should beconstant is also fulfilled when the `saine lis zero; this means,however, that the potential at thel lamp must be constant. f

Fig. 4 shows that by superimposing a properly selected high frequencycurrentover the operatliliy ing D.- C., the characteristic of the lampmay be changed in such manner, that the voltage at the lamp'is constantover the' greater part of the current' 'range employed during themodulationor in other words that the A. C. resistance is practicallyzero. The light intensity of the lamp remains practically unaffected bythe superposedhigh frequency current. i

. Fig. 5 shows diagramrratically the circuit used with the dischargetube. In thisv figure 1 is the output valve of -the receiver amplifier;2 is the discharge tube with a positive luminous column`V and aligatedcathode; 7 represents the anode circuit of the amplifier in whichthe discharge tube 2 is arranged; 5 is an adjustable resistance forcontrolling the `current passing through the discharge tube, 6 is acondenser in shunt to said resistance 5; and 3 indicates a highfrequency generator for capacitycoupling oi.' tube 2 to the highfrequency circuit by means 'of a metallic plate 4.. This high frequencygeneratorgisused for superposng -a high frequency current over theoperating D. C. asshown in Fig. 4. The discharge tube 2 is placed in acasing 9, preferably of heat insulating material. An electric heatingresistance -10 vmay be employed to maintain the desired-operatingtemperature for' the tube 2 vwithinl the casing. I

which occur in any one of the transmission'means may likewise becompensated by a suitable selection of the opeating temperature of thedischarge tube. l c I It is, of course, understood that the invention isnot limited' by the specific description set forth in the above, andthat numerous modifications are quite possible within the scope of theappended claims.

What I claim asmy invention is:

I 1. A method of controlling discharge tubes lled with sodium vapor andoperating with positive column and heated cathode, consisting in soadjusting lthe operatin temperature of the discharge tube that thete'nsity of light is a substantially linear function of the gridpotential of the audion controlling the discharge tube.

2. A method of ,controllingV discharge tubes lledwith sodium vapor andoperating with positivecolumn vand heated cathode, consisting in soadjusting the operating temperaturev of the discharge tube that the A.C. resistance is approximately constant, and thatat the same time atthis temperature the intensity of light is directly proportional to -thecurrent intensity.

3. A method of controlling discharge tubes filled with sodium vapor andoperating with positive column andnheated cathode, consisting in ad- Themaintenance of aconstant A. C. resistance dusting' the Opeiatingtemperature 0f the diS- andof a linear function between 'the intensityof light and the strength of the operating current (characteristic ofintensity of light) make possible a distortinless television reception.But it is als.possible to prevent distortions in the reproduction of thetelevision image by co c pensating for any variation of the A. C.resistance by a ,corresponding non-proportionality of the`characteristic of the intensity of light,-Whichv in `sistance of thelamp has been m ntioned,` it should be understood that always the A. C.resistance was meant as it results from the statically recordedcharacteristic yof the lamp. The A. C'. resistance, however, may alsodepend upon the fre-A quencyor uponA that condition of operationof thelamp which prevailed at the immediately preceding/instant.v This,however, does not-result in any appreciable variation in the workingdiagram of the lamp, which for the sake of simplicityd has beenconsidered to follow th static characteristics, sincevthe' principleis\the same.,

'I'he above considerations and Athe diagrams shown in the Figs. 1-4,apply in the first place" when the discharge tubes-are operated with D.C.' potential. 'I'he same considerations', however,

\ may be applied correspondingly when the dis.-

frequency current `mission means in the system do not operateu chargetubes are operated exclusivelyf'with high When the Jvarioustranslsuperposing a high frequency current over the D. C.for the purposeof acquiring constancy of the A. C; resistance, substantially asdescribed.

5.` In a method for controlling a hot-cathode discharge tube filled withsodium vapor and having a positive luminous colunn, said discharge tubebeing arranged in the anode circuit of the output valve of an amplifier,the step of adjusting the operating temperature of the discharge tube insuch manner that the light intensity of said positive luminous column issubstantially a linear function of` the grid voltage of said outputvalve. l

6. -In a method for controlling a hot-cathode discharge tube filled withsodium vapor and having a positive luminousv column, said discharge tubebeing arranged in the anode circuit of the output lvalve of, anamplifier, theD step of adjusting the operating temperature of thedischarge tube in such manner that the light intensity of said positiveluminous columnis substantially a linear function of the grid voltage ofvsaid output valve, whereby at this operatingtemperature the highestintensity of lightis produced.

GEORG SCHUBERT.

